Sheet processing apparatus and sheet folding method and image forming apparatus

ABSTRACT

According to one embodiment, a sheet processing apparatus pushes, with a folding plate, a sheet bundle held by a stacker into a nip portion formed by a first folding roller and a second folding roller and forms a fold. The first folding roller includes a first folding section configured to come into contact with the second folding roller and form the nip portion and a first groove configured to form a gap between the first groove and the second folding roller in a state in which the first folding section is in contact with the second folding roller. The first groove is formed in a position where an end in the width direction of a sheet bundle of a predetermined size pushed in by the folding plate passes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior U.S. patent application No. 61/528,705, filed on Aug. 29, 2011, and the prior U.S. Patent Application No. 61/528,678, filed on Aug. 29, 2011, and the prior U.S. Patent Application No. 61/528,682, filed on Aug. 29, 2011, and Japanese Patent Application No2012-95258, filed on Apr. 19, 2012, and the entire contents all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a sheet processing apparatus, a sheet folding method, and an image forming apparatus for performing folding of printed sheets.

BACKGROUND

There is a sheet finishing apparatus that is set on a downstream side in a sheet conveying direction of an image forming apparatus such as a copying machine, a printer, or a multi-functional peripheral (MFP) and applies finishing such as punching or stapling to printed sheets. The sheet finishing apparatus includes a function of folding for folding a part of sheets and a function of saddle stapling and saddle folding for folding sheets in the center after stapling the center of the sheets with staples in addition to functions of punching and stapling. The function of saddle stapling and saddle folding can produce (bind) a booklet from printed plural sheets.

In the saddle stapling and saddle folding, the sheet finishing apparatus forms a fold and folds a stapling portion of sheets with a pair of rollers called a folding roller pair after stapling the center of sheets with staples. For example, the sheet finishing apparatus strikes a tabular member called a folding blade against a stapling portion of a sheet bundle and pushes the sheet bundle into a nip portion of the folding roller pair to fold the sheet bundle.

However, in the apparatus in the past, when the sheet bundle is folded in the nip portion of the roller pair, the sheets sometimes wave. In other words, it is likely that the sheet bundle is directly folded by a strong pressing force, whereby creases occur in the sheet bundle.

Therefore, there is a demand for a sheet processing apparatus that more appropriately performs the folding than the sheet processing apparatus including the folding unit in the past.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for explaining a hardware configuration of an image forming apparatus and a sheet processing apparatus according to a first embodiment;

FIG. 2 is a schematic diagram for explaining the configuration of the sheet processing apparatus in the first embodiment;

FIGS. 3A to 3D are schematic diagrams for explaining a lateral alignment member in the first embodiment;

FIG. 4 is a schematic perspective view for explaining a folding unit in the first embodiment;

FIG. 5 is a schematic diagram for explaining a folding roller pair in the first embodiment;

FIG. 6 is a flowchart for explaining folding by the sheet processing apparatus in the first embodiment; and

FIGS. 7A to 7D are schematic diagrams for explaining folding in a second embodiment.

DETAILED DESCRIPTION

Exemplary embodiments are explained in detail below with reference to the accompanying drawings.

First Embodiment

In general, according to one embodiment, a sheet processing apparatus includes: a stacker configured to hold a sheet bundle; a first folding roller; a second folding roller; and a folding plate configured to push the sheet bundle held by the stacker into a nip portion formed by the first folding roller and the second folding roller and forma fold. The first folding roller includes: a first folding section configured to come into contact with the second folding roller and form the nip portion; and a first groove configured to form a gap between the first groove and the second folding roller in a state in which the first folding section is in contact with the second folding roller. The first groove is formed in a position where an end in the width direction of a sheet bundle of a predetermined size pushed in by the folding plate passes.

FIG. 1 is a block diagram for explaining a hardware configuration of an image forming apparatus and a sheet processing apparatus. An image forming apparatus 100 includes a controller 102, a storage device 108, a communication interface (communication I/F) 110, an operation panel 112, a scanner 114 that reads an original document, and a printer (an image forming section) 116 that forms an image. The components of the image forming apparatus 100 are connected via a bus 118.

The controller 102 includes a processor 104 including a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a memory 106. The memory 106 is, for example, a semiconductor memory. The memory 106 includes a ROM (Read Only Memory) having stored therein control programs and the like and a RAM (Random Access Memory) that provides the processor 104 with a temporary work area. The controller 102 controls the operation panel 112, the scanner 114, and the printer 116 on the basis of various computer programs and the like stored in the ROM or the storage device 108. The controller 102 includes a function of correcting or expanding image data. The controller 102 communicates with a controller 202 of a sheet processing apparatus 200.

The storage device 108 stores application programs and an OS. The application programs include computer programs for executing functions of a multifunction peripheral such as a copy function, a print function, a scanner function, a facsimile function, and a network file function. The application programs further include an application for a Web client (a Web browser) and other applications.

The storage device 108 temporarily stores image data of an original document read by the scanner 114, image data acquired via the communication I/F 110, or the like. Further, the storage device 108 appropriately stores software update, a protected electronic document, text data, account information, policy information, and the like. The storage device 108 may be, for example, a magnetic storage device such as a hard disk drive, an optical storage device, a semiconductor storage device (a flash memory, etc.), or an arbitrary combination of these storage devices.

The communication I/F 110 is an interface connected to an external apparatus. The communication I/F 110 is connected to an external apparatus via appropriate radio or wire of IEEE802.15, IEEE802.11, IEEE802.3, IEEE1284, or the like for, for example, Bluetooth (registered trademark), infrared connection, or optical connection. The communication I/F 110 may further include a USB connection section to which a connection terminal of the USB standard is connected and a parallel interface. The controller 102 communicates with a user terminal, a USB device, and other external apparatuses via the communication I/F 110.

The operation panel 112 includes a display section of a touch panel type and various operation keys. The operation keys include, for example, a ten key, a reset key, a stop key, and a start key. The display section displays instruction items concerning printing conditions such as a sheet size, the number of copies, printing density setting, and finishing (stapling or folding). Instructions of the displayed items are input from the display section.

The scanner 114 includes an incorporated scanning and reading unit that reads an original document as an image, a document placing table, and an auto document feeder that conveys the original document to a reading position. The scanning and reading unit of the scanner 114 reads an original document set on the document placing table or the auto document feeder.

The printer 116 includes a publicly-known image forming unit including, for example, a photoconductive drum and a publicly-known developing unit by, for example, toner. The printer 116 forms, using these units, an image corresponding to image data of an original document read by the scanner 114 or an image corresponding to image data sent from the user terminal on a sheet.

The sheet processing apparatus 200 includes the controller 202, a finisher 220, and a saddle unit section 240. The controller 202 includes a processor 204 including a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a memory 206. The memory 206 is, for example, a semiconductor memory. The memory 206 includes a ROM (Read Only Memory) having stored therein control programs and the like and a RAM (Random Access Memory) that provides the processor 204 with a temporary work area. The controller 202 communicates with the controller 102 of the image forming apparatus 100. The controller 202 controls the finisher 220 and the saddle unit section 240 on the basis of information received from the controller 102 and various computer programs and the like stored in the ROM and the like. The saddle unit section 240 includes a stapler 252, a folding unit 258, and a fold reinforcing unit 263.

FIG. 2 is a schematic diagram for explaining the configuration of the sheet processing apparatus. The sheet processing apparatus 200 processes, according to an instruction input from the operation panel 112 or an instruction from the user terminal, a sheet discharged from the image forming apparatus 100. The sheet processing apparatus 200 includes an inlet roller 210, a diverting member 212, the finisher 220, and the saddle unit section 240. The inlet roller 210 carries a sheet, which is carried out from the image forming apparatus 100, into the sheet processing apparatus 200. The diverting member 212 switches, according to a processing content input via the display section of the operation panel 112 of the image forming apparatus 100 shown in FIG. 1, a conveying destination of the sheet carried in by the inlet roller 210 to the finisher 220 or the saddle unit section 240. For example, the finisher 220 sorts a sheet bundle or staples an end of the sheet bundle.

The saddle unit section 240 staples or folds a sheet bundle. The saddle unit section 240 includes plural conveying rollers 242, a carry-out roller 244, a carry-out roller sensor 245, a stacking section 246, the stapler 252, the folding unit 258, the fold reinforcing unit 263, a discharge roller 264, and a sheet bundle stacking tray 266. The conveying rollers 242 convey a sheet to the stacking section 246. The carry-out roller 244 carries out the sheet to the stacking section 246. The carry-out roller sensor 245 detects the conveyed sheet.

The stacking section 246 includes a stack tray 248, stackers 250, and a sensor 251. A sheet is temporarily stacked on the stacking section 246 in an upright position. The stack tray 248 supports the surface of the sheet. The stackers 250 receive the lower end of the sheet. The stackers 250 support the lower end of the sheet stacked in the upright position and align (longitudinally align) the position of the end of the sheet in a conveying direction. The sheet stacked on the stacking section 246 is also aligned in the width direction crossing the sheet conveying direction. The alignment in the width direction (lateral alignment) of the sheet is explained below. The sensor 251 detects that sheet is conveyed to the stackers 250.

The stackers 250 move up and down along the stack tray 248. The stackers 250 adjust the position of sheets stapled by the stapler 252 and the position of sheets folded by the folding unit 258. In the explanation of this embodiment, as an example, the stapling position of the sheets and the folding position of the sheets are assumed to be a center portion in the sheet conveying direction.

Plural (two) staplers 252 are arranged side by side in the width direction of a sheet. The stapler 252 includes a stapler head 254 and an anvil 256. The stapler head 254 and the anvil 256 staple a sheet bundle.

When the stapler 252 staples the sheet bundle, the stackers 250 move to set a stapled position of sheets to a folding position by the folding unit 258. When the stackers 250 stop, the folding unit 258 starts folding.

The folding unit 258 includes a folding plate 260 and a folding roller pair 262. The folding plate 260 stays on standby in a position where the folding plate 260 does not hinder conveyance of a sheet. When a position where a fold should be formed comes to the front of the folding plate 260, the folding plate 260 moves toward the folding roller pair 262. The distal end of the folding plate 260 thrusts the sheet bundle and pushes the sheet bundle to a nip portion of the rotating folding roller pair 262. The folding roller pair 262 compresses, conveys, and folds the sheets pushed by the folding plate 260. The sheet bundle having the fold formed thereon by the folding unit 258 is further conveyed to the fold reinforcing unit 263 provided further on a downstream side of the folding unit 258.

The fold reinforcing unit 263 moves while pressurizing the fold in the width direction crossing the conveying direction of the sheet bundle (a direction along the line of the fold) and reinforces the fold formed by the folding unit 258 (reinforcing). The sheet bundle having the fold reinforced by the fold reinforcing unit 263 is discharged to the sheet bundle stacking tray 266 by the discharge roller 264.

Alignment in the width direction crossing the conveying direction of the sheet stacked on the stacking section 246 (hereinafter, lateral alignment) is explained. FIGS. 3A to 3D are schematic diagrams for explaining a lateral alignment member. The stacking section 246 includes the stackers 250 and a lateral alignment member 300. The lateral alignment member 300 includes a first aligning member 302 a and a second aligning member 302 b, horizontally suspended members 304 a and 304 b, a pinion gear 306, and a motor Ml.

The first aligning member 302 a and the second aligning member 302 b are opposed in parallel to each other. The first aligning member 302 a and the second aligning member 302 b align ends in the width direction (lateral ends) of a sheet stacked on the stackers 250.

The horizontally suspended members 304 a and 304 b are respectively connected to the first aligning member 302 a and the second aligning member 302 b. The horizontally suspended members 304 a and 304 b are opposed in parallel to each other. The horizontally suspended members 304 a and 304 b respectively include racks on opposed surfaces thereof. The pinion gear 306 simultaneously meshes with the racks of the respective horizontally suspended members 304 a and 304 b. The motor M1 rotates the pinion bear 306 via a gear 107. The pinion gear 306 rotates to slide the horizontally suspended members 304 a and 304 b in opposite directions to each other in the width direction of the sheet. The motor M1 may be, for example, a stepping motor. A detecting member 308 detects the positions in the sheet width direction of the first aligning member 302 a and the second aligning member 302 b. The detecting member 308 may be, for example, a micro sensor or a micro actuator. In this embodiment, the detecting member 308 detects that the first aligning member 302 a and the second aligning member 302 b are in home positions (HPs; first positions). A state in which the first aligning member 302 a and the second aligning member 302 b are in the HPs is referred to as a state in which the first aligning member 302 a and the second aligning member 302 b are open in the width direction, i.e., an open state. The positions of the first aligning member 302 a and the second aligning member 302 b are controlled with reference to the HPs according to the number of pulses given to the motor M1 in order to drive the first and second aligning members 302 a and 302 b. When the controller 202 receives an instruction for folding or saddle stapling or saddle folding from the operation panel 112 or an external apparatus, the controller 202 laterally aligns a sheet with the lateral alignment member 300. After the lateral alignment by the lateral alignment member 300, the controller 202 staples a sheet bundle with the stapler 252 or folds the sheet bundle with the folding unit 258.

In FIG. 3A, a state in which the first aligning member 302 a and the second aligning member 302 b are present in the first positions is shown. In ideal conveyance posture, a sheet P1 is conveyed in a state in which the center of a space between the first aligning member 302 a and the second aligning member 302 b and the center in the width direction of the conveyed sheet P1 coincide with each other. The first aligning member 302 a and the second aligning member 302 b are respectively on standby in the first positions away from the lateral ends of the sheet P1, which is conveyed in the ideal conveyance posture, by a first distance. The first distance may be, for example, 15 mm. The first positions may be positions to which the first aligning member 302 a and the second aligning member 302 b are moved from the HPs by applying a predetermined number of pulses to the motor M1 and rotating the motor M1.

The first aligning member 302 a and the second aligning member 302 b move in directions indicated by arrows B in FIG. 3B to come close to the lateral ends of the conveyed sheet P1 and laterally align the sheet P1. For example, the first aligning member 302 a and the second aligning member 302 b move to come close to the lateral ends of the sheet P1 after the lower end of the sheet P1 reaches the position between the first aligning member 302 a and the second aligning member 302 b. For the lateral alignment, for example, the first aligning member 302 a and the second aligning member 302 b move to second positions where the distance between the first aligning member 302 a and the second aligning member 302 b is equal to the length in the width direction of the sheet (a second distance).

After the lateral alignment, as indicated by arrows C in FIG. 3C, the first aligning member 302 a and the second aligning member 302 b move to third positions away from the lateral ends of the sheet P1 by a third distance. The first aligning member 302 a and the second aligning member 302 b wait for the following sheet P2 in the third positions. The third distance may be shorter than the first distance. The third distance may be, for example, 3 mm.

The first aligning member 302 a and the second aligning member 302 b move in directions indicated by arrows D in FIG. 3D to come close to the lateral ends of the conveyed sheet P2 and laterally align a sheet bundle including the sheet P1 and the sheet P2. For example, the first aligning member 302 a and the second aligning member 302 b move to come close to the lateral ends of the sheet P2 after the lower end of the sheet P2 reaches the position between the first aligning member 302 a and the second aligning member 302 b. The first aligning member 302 a and the second aligning member 302 b move to, for example, the second positions in order to perform the lateral alignment. The lateral alignment member 300 repeats the abovementioned actions every time a sheet is conveyed and laterally aligns a sheet bundle including the sheets P1 and P2 and the following sheets.

FIG. 4 is a schematic perspective view for explaining the overall structure of the folding unit 258. In FIG. 4, an arm 270 and a driving section 282 including a groove cam 286 on one side (the near side in the figure) are omitted.

The folding unit 258 includes a folding roller pair 262 that folds a sheet bundle into two, a comb teeth-like folding plate 260 that pushes the sheet bundle into a nip portion of the folding roller pair 262, and a guide member 280 that holds the folding plate 260 to be movable to the folding roller pair 262.

The folding roller pair 262 includes a fixed roller 262 a and a movable roller 262 b. The fixed roller 262 a is fixedly arranged in a not-shown apparatus frame to be rotatable via a shaft. The movable roller 262 b is rotatably supported at one end 270 b of the arm 270 supported in the not-shown apparatus frame to be pivotable about a fulcrum 270 a. The movable roller 262 b can come into contact with and separate from the fixed roller 262 a. A spring 272 is attached to the other end 270 c of the arm 270. The movable roller 262 b urged by the arm 270, which pivots about the fulcrum 270 a, comes into press contact with the fixed roller 262 a and forms a nip portion. The fixed roller 262 a and the movable roller 262 b are rotated by a not-shown driving motor.

The folding plate 260 includes a protrusion section 274 and a shaft 276. The folding plate 260 is slidably held by the guide member 280 via the protrusion section 274 and the shaft 276. The guide member 280 includes a guide groove 280 a for slidably supporting the protrusion section 274 and the shaft 276 and guiding the folding plate 260 to the nip portion of the folding roller pair 262. The driving sections 282 that slide the folding plate 260 are connected to both the ends of the shaft 276.

The driving section 282 includes a cam shaft 284, the groove cam 286 that rotates about the cam shaft 284, and a link member 288. The groove cam 286 includes a groove 286 a. A roller 287 such as a roller follower, which is a contact piece, is rotatably guided into the groove 286 a of the groove cam 286. The roller 287 is attached to the link member 288. A link pivot shaft 290 is provided at one end of the link member 288. The link pivot shaft 290 is attached to the apparatus frame. The groove cam 286 is rotated by a not-shown driving motor connected to one end of the cam shaft 284. When the roller 287 is guided along the groove 286 a according to the rotation of the groove cam 286, the link member 288 repeats a reciprocating action like a pendulum action about the link pivot shaft 290 according to the eccentricity of the groove 286 a. The folding plate 260 slides along the guide groove 280 a of the guide member 280 according to the reciprocating action of the link member 288. The distal end of the folding plate 260 thrusts a sheet bundle and pushes the sheet bundle to the nip portion of the rotating folding roller pair 262. The folding roller pair 262 compresses, conveys, and folds sheets pushed by the folding plate 260.

FIG. 5 is a schematic diagram for explaining the folding roller pair 262. The fixed roller 262 a and the movable roller 262 b of the folding roller pair 262 are formed at the length equal to the width of a largest sheet that can be processed by the sheet processing apparatus.

The fixed roller 262 a of the folding roller pair 262 includes first folding sections 292, which are areas having a roller diameter of r1, and first grooves 293, which are areas having a roller diameter of r2 (r1>r2). The first folding sections 292 come into contact with the movable roller 262 b and form nip portions. The first grooves 293 form gaps between the first grooves 293 and the movable roller 262 b in a state in which the first folding sections 292 are in contact with the movable roller 262 b.

The movable roller 262 b includes second folding sections 294, which are areas having a roller diameter of r1, and second grooves 295, which are areas having a roller diameter of r2 (r1>r2). The second folding sections 294 come into contact with the first folding sections 292 of the fixed roller 262 a and form nip portions. The second grooves 295 form gaps in a state in which the first folding sections 292 and the second folding sections 294 form the nip portions. The first grooves 293 and the second grooves 295, which form the gaps, are arranged such that the distal end of the comb teeth-like folding plate 260 enters the gaps.

The first grooves 293 and the second grooves 295 are formed to correspond to the size of sheets pushed in by the folding plate 260. In other words, the first grooves 293 and the second grooves 295 are formed in positions where ends in the width direction of a sheet of a predetermined size crossing the sheet conveying direction pass during folding. If the predetermined size is plural sizes, plural first grooves 293 and plural second grooves 295 are formed for each of the predetermined sizes.

When a sheet bundle is pushed into the nip portions of the folding roller pair 262 by the folding plate 260, force applied to sheets is different in a pressed portion and a portion nipped by the folding roller pair 262. After forming a fold on the sheet bundle with the folding roller pair 262, the sheet bundle is conveyed by the folding roller pair 262. Consequently, it is likely that a bend occurs during the conveyance and creases are formed on the sheets. In particular, in a state in which the ends in the width direction of the sheets are nipped, the bend may not be able to sufficiently escape.

Therefore, in the fixed roller 262 a and the movable roller 262 b of the folding roller pair 262 in this embodiment, grooves are formed to prevent the ends in the width direction of the sheet bundle from being nipped by the folding roller pair 262. Portions of the sheet bundle several millimeters from the sheet ends are prevented from being nipped by the rollers, whereby the bend that occurs in the sheet bundle surely escape from the ends of the sheet bundle. Therefore, it is possible to prevent the occurrence of the creases.

Modification of the First Embodiment

In the first embodiment, the sheet ends are not nipped by the folding roller pair 262. However, in a modification of the first embodiment, sheet ends of a sheet other than the sheet of the predetermined size for which the corresponding grooves are formed (hereinafter, irregular-size sheet) are not nipped either.

FIG. 6 is a flowchart for explaining folding in this modification. In ACT 601, the controller (an acquiring section) 202 acquires a size of a sheet conveyed to the stackers 250. The controller 202 may acquire the sheet size from the controller 102 of the image forming apparatus 100, may detect the sheet size using a detecting member provided in a conveying path of the sheet processing apparatus 200, or may detect the sheet size using a detecting member that detects ends of the sheet in a publicly-known punch unit. Alternatively, a detecting member that detects the size of the sheet conveyed to the stackers 250 may be arranged.

In ACT 602, the controller 202 drives the lateral alignment member 300 to align the width direction of the sheet conveyed to the stackers 250. The controller 202 determines whether a last sheet of a sheet bundle to be folded is conveyed to the stackers 250 (ACT 603). If the sheet is not the last sheet of the sheet bundle (No in ACT 603), the controller 202 returns to ACT 602 and performs lateral alignment every time a sheet is conveyed to the stackers 250.

On the other hand, if the lateral alignment is completed in a state in which the last sheet of the sheet bundle is conveyed to the stackers 250 (Yes in ACT 603), the controller 202 determines, on the basis of acquired information concerning the sheet size, whether sheets are sheets of the predetermined size corresponding to the grooves formed in the rollers of the folding roller pair 262 (ACT 604). If the sheets are the sheets of the predetermined size (Yes in ACT 604), the controller 202 pushes laterally-aligned sheets into the folding roller pair 262 with the folding plate 260 and performs folding (ACT 605).

On the other hand, if the sheet size of the sheet bundle stacked on the stackers 250 is not the predetermined size (No in ACT 604), the controller 202 slides the first aligning member 302 a and the second aligning member 302 b in the sheet width direction and shifts the sheet bundle (ACT 606). The controller 202 shifts the sheet bundle such that at least one of both ends of a sheet bundle of an irregular size is located in the first groove 293 and the second groove 295 of the folding roller pair 262. After shifting the sheet bundle in the width direction via the lateral alignment member 300, the controller 202 pushes the sheet bundle into the folding roller pair 262 with the folding plate 260 and performs the folding (ACT 605). At least one of both the ends in the width direction of the sheet bundle passes the gap formed by the first groove 293 and the second groove 295.

In this modification, even if the irregular-size sheets other than the sheets of the predetermined size corresponding to the grooves formed in the rollers of the folding roller pair 262 are processed, the position of the sheet bundle is adjusted such that at least one of both the ends of the sheet bundle is located in the grooves of the folding roller pair 262. Consequently, it is possible to realize the same effects as the effects of the first embodiment.

Second Embodiment

FIGS. 7A to 7D are schematic diagrams for explaining folding in a second embodiment. As shown in FIG. 7A, the folding plate 260 of the sheet processing apparatus 200 pushes a sheet bundle stacked on the stackers 250 into the nip portion of the folding roller pair 262. Subsequently, as shown in FIG. 7B, the folding roller pair 262 presses the sheet bundle, which is pushed in by the folding plate 260, with the fixed roller 262 a and the movable roller 262 b and forms a fold on the sheet bundle.

As shown in FIG. 7C, after forming the fold on the sheet bundle with the folding roller pair 262, the controller 202 of the sheet processing apparatus 200 according to this embodiment once displaces the movable roller 262 b in the direction opposite to the fixed roller 262 a. In other words, the controller 202 reduces or eliminates a nip (a fold load) of the sheet bundle by the folding roller pair 262 to thereby allow a bend of the sheet bundle to escape and prevent occurrence of creases. The movable roller 262 b does not have to be separated from the sheet bundle. For example, the movable roller 262 b may be displaced such that a pressing force of the movable roller 262 b on the fixed roller 262 a decreases to be smaller than a pressing force (a load) for forming a fold.

As shown in FIG. 7D, the controller 202 displaces the movable roller 262 b to the fixed roller 262 a side and presses the sheet bundle, on which the fold is formed, with the fixed roller 262 a and the movable roller 262 b again. The fixed roller 262 a and the movable roller 262 b convey the nipped sheet bundle downstream in the sheet conveying direction.

With the sheet processing apparatus according to this embodiment, it is possible to allow a bend that occurs in a sheet bundle to escape and prevent occurrence of creases.

According to at least one of the embodiments explained above, it is possible to perform more appropriate folding.

An entity that executes the operations in the embodiments is an entity related to a computer such as hardware, a complex of the hardware and software, the software, and the software being executed. The entity that executes the operations is a process executed on a processor, the processor, an object, an execution file, a thread, a computer program, and the computer but is not limited to these. The process or the thread may be caused to play plural entities that execute the operations.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of invention. Indeed, the novel apparatus described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

1. A sheet processing apparatus comprising: a stacker configured to hold a sheet bundle; and a folding plate configured to push the sheet bundle held by the stacker into a nip portion formed by the first folding roller and the second folding roller, wherein the first folding roller includes a first folding section and a first groove, the first folding section being configured to come into contact with the second folding roller and form the nip portion, and the first groove being configured to form a gap between the first groove and the second folding roller in a state in which the first folding section is in contact with the second folding roller and being formed in a position where an end in a width direction of a sheet bundle of a predetermined size, on which a fold is formed, passes, and the second folding roller forms a fold on the sheet bundle in cooperation with the first folding roller.
 2. The apparatus according to claim 1, wherein the second folding roller includes: a second folding section configured to come into contact with the first folding section of the first folding roller and form the nip portion; and a second groove configured to form the gap between the second groove and the first folding roller in a state in which the first folding section and the second folding section are in contact with each other.
 3. The apparatus according to claim 2, wherein the second groove is formed in a position where the end in the width direction of the sheet bundle of the predetermined size pushed in by the folding plate passes.
 4. The apparatus according to claim 3, wherein the predetermined size is a plurality of sizes, and a plurality of the first and second grooves are formed for each of the predetermined sizes.
 5. The apparatus according to claim 4, further comprising an aligning member configured to align, before the sheet bundle is pushed by the folding plate, a width direction of the sheet bundle stacked by the stacker.
 6. The apparatus according to claim 5, further comprising: an acquiring section configured to acquire a size of a sheet stacked on the stacker; and a controller configured to determine whether the size of the sheet acquired by the acquiring section corresponds to the predetermined size and, if the acquired size of the sheet does not correspond to the predetermined size, before the folding plate pushes the sheet bundle into the nip portion, move the sheet bundle to a predetermined position where at least one of both ends in a width direction of the sheet bundle passes the gap.
 7. The apparatus according to claim 6, wherein the controller moves the sheet bundle to the predetermined position via the aligning member.
 8. A sheet processing method for a sheet processing apparatus including: a first folding roller including a folding section configured to come into contact with a second folding roller and form, in a state in which the folding section is in contact with the second folding roller, a nip portion and a groove configured to form a gap between the groove and the second folding roller and in a position where an end in a width direction of a sheet bundle of a predetermined size passes; and a folding plate configured to push a sheet bundle held by a stacker into the nip portion and form a fold, the method comprising: acquiring a size of a sheet of the sheet bundle; determining whether the acquired size of the sheet corresponds to the predetermined size; and moving, if the acquired size of the sheet does not correspond to the predetermined size, before the folding plate pushes the sheet bundle into the nip portion, the sheet bundle to a predetermined position where at least one of both ends in a width direction of the sheet bundle passes the gap.
 9. The method according to claim 8, wherein the second folding roller includes: a second folding section configured to come into contact with the first folding section of the first folding roller and form the nip portion; and a second groove configured to form the gap between the second groove and the first folding roller in a state in which the first folding section and the second folding section are in contact with each other.
 10. The method according to claim 8, further comprising aligning a width direction of a sheet bundle stacked by the stacker before the folding plate pushes the sheet bundle.
 11. The method according to claim 10, further comprising moving the sheet bundle to the predetermined position with an aligning member configured to align the width direction of the sheet bundle stacked by the stacker.
 12. An image forming apparatus comprising: an image forming section configured to form an image on a sheet; a stacker configured to hold a sheet bundle subjected to image formation; a folding plate configured to push the sheet bundle held by the stacker into a nip portion formed by the first folding roller and the second folding roller, wherein the first folding roller includes a first folding section and a first groove, the first folding section being configured to come into contact with the second folding roller and form the nip portion, and the first groove being configured to form a gap between the first groove and the second folding roller in a state in which the first folding section is in contact with the second folding roller and being formed in a position where an end in a width direction of a sheet bundle of a predetermined size, on which a fold is formed, passes, and the second folding roller forms a fold on the sheet bundle in cooperation with the first folding roller.
 13. The apparatus according to claim 12, wherein the second folding roller includes: a second folding section configured to come into contact with the first folding section of the first folding roller and form the nip portion; and a second groove configured to form the gap between the second groove and the first folding roller in a state in which the first folding section and the second folding section are in contact with each other.
 14. The apparatus according to claim 13, wherein the second groove is formed in a position where the end in the width direction of the sheet bundle of the predetermined size pushed in by the folding plate passes.
 15. The apparatus according to claim 14, wherein the predetermined size is a plurality of sizes, and a plurality of the first and second grooves are formed for each of the predetermined sizes.
 16. The apparatus according to claim 15, further comprising an aligning member configured to align, before the sheet bundle is pushed by the folding plate, a width direction of the sheet bundle stacked by the stacker.
 17. The apparatus according to claim 16, further comprising: an acquiring section configured to acquire a size of a sheet stacked on the stacker; and a controller configured to determine whether the size of the sheet acquired by the acquiring section corresponds to the predetermined size and, if the acquired size of the sheet does not correspond to the predetermined size, before the folding plate pushes the sheet bundle into the nip portion, move the sheet bundle to a predetermined position where at least one of both ends in a width direction of the sheet bundle passes the gap.
 18. The apparatus according to claim 17, wherein the controller moves the sheet bundle to the predetermined position via the aligning member. 